Video/graphics overlay techniques mentioned above enable to select graphics and display the selected graphics in accordance with a language setting or display setting of a reproduction apparatus. Also, the video/graphics overlay techniques enable to select whether or not to display graphics according to need. Because of their capability of offering such selections, the video/graphics overlay techniques are employed in player models of DVD-Video and ETSI EN 300 743. In these standards, the graphics stream is an arrangement of PES packets. The PES packets can be classified into two types: a PES packet carrying control information and a PES packet carrying graphics data which represents graphics. The control information is arranged before the graphics data, and one pair of control information and graphics data produces one graphics display. In more detail, the reproduction apparatus reads the control information and the graphics data in sequence, decodes the control information, and also decodes the graphics data to generate uncompressed graphics. The reproduction apparatus displays the uncompressed graphics with a desired presentation timing, according to a decoding result of the control information.
According to this technique, decoding of graphics data needs to be performed for each graphics display. This being so, a time interval from one graphics display to the next graphics display depends on a time period required for a decoding process of graphics data. If graphics has a higher resolution and a decoding process of graphics data takes a longer time, a time interval with which graphics is updated lengthens.
In the case of subtitling in a movie film or the like where graphics is updated with a time interval of 2 to 3 seconds, proper graphics displays can still be produced even if graphics has a higher resolution and decoding of graphics data takes a longer time. In the case where graphics is used specially as a means of amusement, however, the need to shorten the graphics update interval arises.
For example, the use of graphics for amusement purposes includes such applications where graphics representing a dialog of a character is moved to attract the viewer's attention or varied in color to surprise the viewer. Producers of video content such as variety shows are especially eager to adopt such graphics displays.
To realize smooth movements of graphics, however, an operation of decoding graphics data and presenting graphics needs to be performed within a short time of one frame period ( 1/29.97 seconds in NTSC). Repeating this operation of decoding graphics data and presenting graphics within each frame period requires a tremendous load, and is hard to be realized with hardware specifications of reproduction apparatuses that are expected to be provided at low cost.
The aforementioned graphics movements and variations in color can be achieved by overlaying graphics on each frame of video beforehand so that graphics forms a part of a picture pattern of each frame. This method of overlaying graphics on each frame beforehand, however, lacks flexibility of being able to selectively display graphics in accordance with a language setting or display setting of a reproduction apparatus, and therefore does not have much future potential.